Nanofiber manufacturing apparatus and method of manufacturing nanofibers

ABSTRACT

A nanofiber manufacturing apparatus ( 100 ) which produces nanofibers ( 301 ) by electrically stretching a solution ( 300 ) in space. The apparatus includes: an effusing body ( 115 ) having effusing holes ( 118 ) for effusing the solution into the space, a tip part ( 116 ) in which openings ( 119 ) are arranged at given intervals, and two side wall parts ( 117 ) provided so as to extend from both sides of the tip part so that the effusing holes are located between the side wall parts and the distance between the side wall parts increases with the distance from the tip part; a charging electrode ( 121 ) disposed at a given distance from the effusing body; and a charging power supply ( 122 ) which applies a given voltage between the effusing body and the charging electrode.

This application is a divisional of application Ser. No. 13/258,128,which is the National Stage of International Application No.PCT/JP2010/005037, filed Aug. 11, 2010.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a nanofiber manufacturing apparatuswhich produces fibers having diameters of submicron order or nanometerorder (referred to as nanofibers in this description) by electrostaticstretching, and a method of manufacturing nanofibers,

2. Description of the Related Art

There is a known method of manufacturing filamentous (fibrous)substances containing a resin and having a submicron- or nanometer-scalediameter by making use of electrostatic stretching (electrospinning).

The electrostatic stretching is a method of manufacturing nanofibers. Inthe method, a solution prepared by dispersing or dissolving a solutesuch as a resin in a solvent is effused (ejected) into space through anozzle or the like, and the solution is charged and electricallystretched in flight so that nanofibers are produced.

The following describes the electrostatic stretching more specifically.The solvent gradually evaporates from the charged solution while thesolution effused into space is in flight. The volume of the solution inflight thus gradually decreases while the charges imparted to thesolution stays in the solution. As a result, the charge density of thesolution in flight gradually increases. The solvent ongoingly evaporatesand the charge density of the solution further increases, and thesolution is explosively stretched into a line when the Coulomb forcegenerated in the solution and repulsive to the surface tension of thesolution surpasses the surface tension. This is how the electrostaticstretching occurs. The electrostatic stretching exponentially occurs inspace one after another so that nanofibers having diameters ofsub-micron orders or nanometer orders are in produced.

One of the specific problems with an apparatus for manufacturingnanofibers by such electrostatic stretching is the difficulty ofincreasing productivity. For example, effusing solution throughcylindrical nozzles arranged in a matrix increases a production rate perunit time and unit area so that productivity of nanofibers is increased.However, although the production rate of nanofibers per unit area can befurther increased by narrowing intervals between the nozzles, narrowerintervals may cause interference of electric fields between adjacentnozzles, which results in defects in generated nanofibers. In order tosolve the problem, the apparatus according to JP2008-174867 includesseparators which are arranged in a grid pattern among the nozzles and towhich alternating voltage is applied so that interference of electricfields is prevented.

SUMMARY OF INVENTION 1. Technical Problem

However, in the technique disclosed in JP2008-174867, the intervalsbetween the nozzles need to have a width required to accommodate theseparators. As a result, productivity decreases for the increase in theintervals between the nozzles. In addition, because each of the nozzlesare surrounded by the separators, the space surrounded by the separatorsis likely to have resident charged vapor which may cause a negativeimpact on resulting nanofibers. In addition, because it is difficult toprovide solution to the nozzles at an even pressure, the quality of theresulting nanofibers may not be consistent.

Furthermore, the inventors of the present invention found that the ionicwind was generated from the external walls of the nozzles and the ionicwind causes a negative impact on resulting nanofibers even when suchseparators are provided.

The ionic wind is considered to be generated in the phenomenon describedas follows. First, when charges accumulate on a part of an externalwall, air around the part is ionized. Next, the ionized air repelscharges on the wall, so that air containing ions flows so that ionicwind is generated. The inventors have also found that such ionic wind islikely to be generated at specific parts of the external wall, such asthe tip of a protrusion and the tip of a corner part.

In addition, when the ionic wind encounters a solution flying in space,the flight path of the solution and the nanofiber being produced isdisrupted or the charging of the solution is adversely affected. As aresult, the quality of the resulting nanofibers deteriorates and theproductivity of the nanofibers decreases.

The present invention, based on considerations of the problems and thefindings, has an object of providing a nanofiber manufacturing apparatusand a method of manufacturing nanofibers using which occurrence ofinterference of electric fields is prevented to keep a high productionrate of nanofibers per unit hour and unit area and the impact of theionic wind is limited so that nanofibers of high and consistent qualitycan be produced.

2. Solution to Problem

In order to achieve the object, the nanofiber manufacturing apparatusaccording to an aspect of the present invention produces nanofibers byelectrically stretching a solution in space, and includes: an effusingbody having, a plurality of effusing holes for effusing the solutioninto the space, a tip part in which openings at ends of the effusingholes are one-dimensionally arranged at given intervals, and two sidewall parts provided extending from both sides of the tip part so thatthe effusing holes are located between the side wall parts and distancebetween the side wall parts increases with distance from the tip part; acharging electrode disposed at a given distance from the effusing body;and a charging power supply which applies a given voltage between theeffusing body and the charging electrode.

With this, the spaces between the openings of the effusing holesarranged at given intervals are filled with the tip part so thatinterference of electric fields is unlikely to occur. As a result, theintervals between the openings from which a solution effuses areminimized and the production rate of nanofibers per unit area isincreased.

In addition, in the structure in which the distance between the sidewall parts of the effusing body is smallest at the tip part andincreases with the distance from the openings, only limited ionic windgenerated at the side wall parts flies in a direction such that theionic wind causes a negative impact on the resulting nanofibers. Inaddition, ionic wind is unlikely to be generated at the surfaces of theside wall parts extending along the direction in which the openings arearranged. The effusing body can thus limit the effects of ionic wind onnanofibers.

Furthermore, the effusing body may further have a storage tank which isconnected to the effusing holes, stores the solution supplied from thesupply unit, and supplies the solution to the effusing holes at a time.

With this, the solution supplied from the supply unit is first stored inthe supply unit and then supplied to the effusing holes, so that thesolution is supplied to the effusing holes at pressures as uniform aspossible. In addition, such an effect is achieved by a simple structurewithout additional parts.

Furthermore, the tip part may have a rectangular shape having a widthwhich is larger than a diameter of the openings provided in the tippart.

With this, Taylor cones (for details, see Embodiment) generated aroundthe openings are retained more favorably by the tip part. The solutionthinly effuses from the Taylor cones, and then is electrostaticallystretched. The joints between the effusing holes and the tip part arethus covered by the solution, so that generation of ionic wind islimited.

Furthermore, the nanofiber manufacturing apparatus may further includean accumulating unit on which the nanofibers produced in the space areaccumulated; and an attracting unit configured to attract the nanofibersto the accumulating unit.

With this, nanofibers to be accumulated are selectively limited so thatfunctional material can be produced.

Furthermore, the nanofiber manufacturing apparatus may further include amoving unit configured to move at least one of the effusing body and theaccumulating unit relative to each other.

With this, nanofibers can be accumulated evenly over a wide area.

Furthermore, the effusing body preferably has a structure which allows(i) disassembly of the effusing body into parts to expose surfacesforming the effusing holes and (ii) re-assembly of the parts into theeffusing body.

The effusing body has increased maintainability.

Furthermore, in order to achieve the object, the method of manufacturingnanofibers according to an aspect of the present invention byelectrically stretching a solution in space includes: effusing thesolution from an effusing body into the space, the effusing body having:a plurality of effusing holes; a tip part in which openings at ends ofthe effusing holes are provided at given intervals to formone-dimensional array; and two side wall parts provided to extend alongboth sides of the array of the effusing holes and rise from the tip partsuch that distance between the side wall parts increases in going awayfrom the tip part; and applying a given voltage between the effusingbody and a charging electrode disposed at a given distance from theeffusing body.

With this, the spaces between the openings of the effusing holesarranged at given intervals are filled with the tip part so thatinterference of electric fields is less likely to occur. As a result,the intervals between the openings from which a solution effuses areminimized and a production rate of nanofibers per unit area isincreased.

In addition, in the structure in which the distance between the sidewall parts of the effusing body is smallest at the tip part andincreases with distance from the openings, only limited ionic windgenerated at the side wall parts flies in a direction such that theionic wind causes a negative impact on the resulting nanofibers. Inaddition, ionic wind is not likely to be generated at the surfaces ofthe side wall parts extending along the direction in which the openingsare arranged. The effusing body can thus limit the effects of ionic windon nanofibers.

3. Advantageous Effects of the Invention

According to the present invention, productivity of nanofibers andquality of the nanofibers are increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a nanofiber manufacturingapparatus.

FIG. 2 is a perspective view illustrating a cutaway of the effusingbody.

FIG. 3 is a perspective view illustrating the effusing body viewed fromthe side of the tip part.

FIGS. 4( a)-4(b) are perspective views illustrating variations of thetip part.

FIG. 5 is a perspective view illustrating another embodiment of thenanofiber manufacturing apparatus.

FIG. 6 is a perspective view illustrating an effusing body which allowsdisassembly into parts.

FIG. 7 is a perspective view illustrating a cutaway of an effusing bodyhaving a different shape.

FIG. 8 is a perspective view illustrating a cutaway of an effusing bodyhaving a different shape.

FIG. 9 is a perspective view illustrating a cutaway of an effusing bodyhaving a different shape.

FIG. 10 is a perspective view illustrating a cutaway of an effusing inbody having a different shape.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following describes a nanofiber manufacturing apparatus and a methodof manufacturing nanofibers according to the present invention withreference to the drawings.

FIG. 1 is a perspective view illustrating a nanofiber manufacturingapparatus.

As shown in FIG. 1, a nanofiber manufacturing apparatus 100, which is anapparatus for manufacturing nanofibers 301 by electrically stretching asolution 300 in space, includes an effusing body 115, a supply unit 107,a charging electrode 121, and a charging power supply 122. In anembodiment of the present invention, the nanofiber manufacturingapparatus 100 further includes an accumulating unit 128 and anattracting unit 104. In addition, the nanofiber manufacturing apparatus100 includes a moving unit 129.

FIG. 2 is a perspective view illustrating a cutaway of the effusingbody.

The effusing body 115 is a member for effusing the solution 300 intospace by pressure of the solution 300 (and the gravity in some cases).The effusing body 115 has effusing holes 118, a tip part 116, side wallparts 117, and a storage tank 113. The effusing body 115 also includes aconductive member on at least part of the surface in contact with thesolution 300 so as to function as an electrode to provide charges to thesolution 300 which effuses from the effusing body 115. In the presentembodiment, the effusing body 115 is made of metal in whole. The metalto be used as a material for the effusing body 115 is not limited to aspecific type of metal and may be any conductive metal such as brass orstainless steel.

The effusing holes 118 are holes provided in the effusing body 115 andallow the solution 300 to effuse therethrough in a given direction. Theopenings 119 at the ends of the respective effusing holes 118 areone-dimensionally arranged at constant intervals. In the presentembodiment, the effusing holes 118 are arranged such that the openings119 lineally align to be coplanar and that the axels of the effusingholes 118 are perpendicular to the direction in which the openings 119align.

The effusing holes 118 do not have a specifically limited length ordiameter and are formed to have a shape appropriate for conditions suchas the viscosity of the solution 300. Specifically, the effusing holes118 preferably have a length within a range from 1 mm to 5 mm and adiameter within a range from 0.1 mm to 2 mm. The shape of the effusingholes 118 is not limited to a cylindrical shape and any shape may beselected for the shape as necessary. In particular, the shape of theopenings 119 is not limited to a circular shape and may be a polygonalshape such as a triangle or a quadrilateral, and even a concave shapesuch as a star polygon.

All the intervals between the openings 119 may be the same.Alternatively, the intervals between the openings 119 in the end partsof the effusing body 115 may be larger (or smaller) than the intervalsbetween the openings 119 in the middle part of the effusing body 115 asnecessary. As far as the inventors have so far found, the pitchesbetween the openings 119 having a diameter of 0.3 mm can be as small as2.5 mm. The diameter and pitch of the openings 119 may be in changeddepending on conditions such as the viscosity of the solution 300.

The arrangement of the openings 119 is not limited to a lineararrangement and may be any one-dimensional arrangement. Here,“one-dimensional” means that the openings 119 do not align in thedirection of the width of a rectangle outlining a region in which allthe openings 119 are included with no margin along the sides of theregion. The rectangular region including the openings 119 is astrip-shaped region. In this meaning, the opening 119 may be arranged ina zigzag manner or along a wavy line such as a sine curve.

The tip part 116 is a part of the effusing body 115. The openings 119 ofthe effusing holes 118 are provided in the tip part 116 at regularintervals. The tip part 116 has a smooth surface which fills theintervals between the openings 119. In the present embodiment, the tippart 116 has an elongated rectangular flat face on its surface, and isdesigned to have a width larger than the diameter of the openings 119.The width of the tip part 116 depends on the diameter of the effusingholes 118. The tip part 116, for a specific example, is preferablydesigned to have a width larger than 1 mm in consideration of the basesof Taylor cones 303 (described later, see FIG. 3) having a diameter of 1mm.

The tip part 116 having a flat surface is present all around theopenings 119 so that Taylor cones 303 are formed around the respectiveopenings 119 as shown in FIG. 3. The Taylor cones 303 are cones of thesolution. They are considered to form due to the viscosity of thesolution 300. Each of the Taylor cones 303 has a conical shape with acircular base having a diameter larger than the opening 119. The Taylorcones 303 attach to the tip part 116 of the effusing body 115 so in asto cover the openings 119. The solution 300 thinly effuses into spacefrom each of the Taylor cones 303. The Taylor cones 303 prevent theopenings 119 from being in direct contact with air so that ionic windgenerated from the openings 119 can be prevented.

It is to be noted that the shape of the tip part 116 is not limited to ashape having a flat rectangular surface and that the Taylor cones 303may form on a non-flat surface. For example, the tip part 116 may have acurved surface as shown in FIG. 4( a). Alternatively, the tip part 116may have two flat surfaces which meet each other at their ends as shownin FIG. 4( b).

Alternatively, when the openings 119 are arranged in a zigzag manner oralong a wavy line as mentioned above, the tip part 116 may be a straightstrip-shaped part or may have a shape following the array of theopenings 119, such as a zigzag shape or a wavy shape.

The tip part 116 thus has a surface which fills the intervals betweenthe openings 119 (two surfaces which fill the intervals in FIG. 4( b) asdescribed above) so that interference of electric fields between nozzlesarranged close to each other can be prevented. In addition, generationof ionic wind between the openings 119 is also prevented. Therefore,favorable nanofibers 301 can be produced even when the openings 119 arearranged with narrower intervals. As a result, productivity ofnanofibers 301 per unit time and unit area can be increased.

In addition, because the tip parts 116 can retain the Taylor cones 303in a favorable status, generation of ionic wind is prevented so thatquality and productivity of the nanofibers 301 can be improved.

Referring to FIG. 2, the side wall parts 117 are two walls provided soas to have the effusing holes 118 located therebetween, and are parts ofthe effusing body 115, extending upward from the tip part 116. Inaddition, the side wall parts 117 extend along the direction in whichthe effusing holes 118 are arranged so that all the effusing holes 118are located between the two side wall parts 117. In addition, the sidewall parts 117 are provided so that the distance therebetween increaseswith distance from the tip part 116 as shown in FIG. 2. The more acutethe angle between the side wall parts 117 is, the more charges can beconcentrated at the tip part, and thereby high-quality nanofibers 301can be produced from the solution 300 having a high charge density. Onthe other hand, the more acute the angle between the side wall parts 117is, the smaller the volume of the storage tank 113 of the effusing body115 and the more difficult the processing for providing the effusingbody 115 with the storage tank 113 is. Taking these conditions intoconsiderations, a preferable angle between the side wall parts 117 isapproximately 60 degrees. It is to be noted that the angle between theside wall parts 117 of the effusing body 115 is not limited to this.

As shown in FIG. 4( a) and FIG. 4( b), there is no definite boundarybetween the tip part 116 and the side wall parts 117. In addition, theshape of the side wall parts 117 is not limited to a flat shape. Theside wall parts 117 may have a curved shape. For example, in the casewhere the effusing hales 118 are provided in the circumferential wall ofthe cylindrical effusing body 115 as shown in FIG. 7, the part where theeffusing holes 118 are provided in the circumferential wall of thecylindrical effusing body 115 serves as the tip part and the parts onboth sides of the tip part (the part where the effusing holes 118 areprovided) serve as the side wall parts 117. In this case, a member to beincluded in the effusing body 115 is easily obtainable and the membercan be easily processed into the effusing body 115. On the other hand,the effusing body 115 having such a shape concentrates fewer charges atthe tip part 116 than the effusing body 115 having another shape (forexample, the shape of the effusing body 115 as shown in FIG. 2), but thedifference can be compensated by using a higher voltage or changing theposition or shape of the charging electrode 121. Alternatively, theeffusing body 115 may have a flat shape in the side wall parts 117 and acylindrical shape in the part where the storage tank 113 is provided asshown in FIG. 8. Alternatively, the side wall parts 117 on both sides ofthe tip part 116 may form a curved shape such that the distance betweenthe side wall parts 117 increases with distance from the tip part 116,and the part where the storage tank 113 is provided may have arectangular-tubular shape as shown in FIG. 9. Alternatively, theeffusing body 115 may be a cylinder having an oval cross section asshown in FIG. 10.

The side wall parts 117 as illustrated above are provided so that thedistance therebetween increases with distance from the tip part 116, andextend in a direction along the array of the effusing holes 118 locatedbetween the side wall parts 117. The effusing body 115 obtained bycombining the parts of the above-illustrated variations of the effusingbody 115 is also within the scope of the present invention. The sidewall parts 117 are part of the effusing body 115 and have continuousfaces such that the distance therebetween increases with the distancefrom the tip part 116.

The side wall parts 117 and the tip part 116 preferably have smoothsurfaces overall and have minimum specific parts (but necessarily havethe openings 119) such that generation of ionic wind is prevented.

The effusing body 115 has the side wall parts 117 such that generationof ionic wind is prevented. In addition, even when ionic wind isgenerated, the wind is blown off in a direction such that the ionic winddoes not cross the solution 300 effusing into space. It is thus possibleto produce nanofibers 301 in stable conditions with no impact of theionic wind.

The arrangement in which the side wall parts 117 come closer to eachother toward the tip part 116 makes it easy to concentrate charges atthe tip part 116, and thus charges can be efficiently supplied to thesolution 300.

In addition, as the space around the openings 119 is widely open, it ispossible to prevent charged vapor from congesting around the openings119. Viewed from another viewpoint, such congestion of charged vapor isactively prevented by a flow of gas along the side wall parts 117.

In addition, for example, when wind is generated which blows from nearthe openings 119 toward the downstream of the effusion of the solution300, charged vapor and ionic wind are driven off from the side wallparts 117 in the (downward) direction along the flight path of thesolution 300. As a result, quality of the resulting nanofibers 301 canbe increased.

As shown in FIG. 2, the storage tank 113 is provided inside the effusingbody 115 and stores the solution 300 supplied from the supply unit 107(see FIG. 1). The storage tank 113 is connected to the effusing holes118 and supplies the solution 300 to the effusing hole 118. In thepresent embodiment, one storage tank 113 is provided in the effusingbody 115, extending from one of the ends of the effusing body 115 to theother end thereof so that the storage tank 113 is connected in to allthe effusing holes 118.

The storage tank 113 thus has a function of temporarily storing thesolution 300 near the effusing holes 118 and a function of supplying thesolution 300 to the effusing holes 118 at an even pressure so that thesolution 300 effuses from the effusing holes 118 in a uniform status. Asa result, spatial unevenness in quality of the resulting nanofibers 301is avoided.

The supply unit 107 includes a container 151, a pump (not shown in thedrawing), and a guide tube 114 as shown in FIG. 1 to supply the solution300 to the effusing body 115. The container 151 stores the solution 300in large quantity. The pump transfers the solution 300 with a givenpressure. The guide tube guides the solution 300.

The charging electrode 121 is disposed at a given distance from theeffusing body 115 and induces charges into the effusing body 115 byhaving a high voltage or a low voltage compared to the effusing body115. In the present embodiment, the charging electrode 121 is disposedat a position facing the tip part 116 of the effusing body 115 and isgrounded so that the charging electrode 121 functions as an attractingunit 104 which attracts the nanofibers 301. When a positive voltage isapplied to the effusing body 115, negative charges are induced into thecharging electrode 121. When a negative voltage is applied to theeffusing body 115, positive charges are induced into the chargingelectrode 121.

The charging power supply 122 is a power supply capable of applying ahigh voltage to the effusing body 115. Generally, the charging powersupply 122 is preferably a direct-current power supply. In particular,use of a direct current is preferable when the charging power supply 122is free from the impact of the charge polarity of the resultingnanofibers 301 or when the nanofibers 301 are attracted by an electrodeto which a potential of a reverse polarity is applied. When the chargingpower supply 122 is a direct-current power supply, the voltage which thecharging power supply 122 applies to the charging electrode 121 ispreferably within a range from 5 kV to 100 kV.

The charging electrode 121 is grounded by setting one of the electrodesof the charging power supply 122 at a ground potential as in the presentembodiment even when the charging electrode 121 is relatively large, sothat safety of the nanofiber manufacturing apparatus is improved.

The solution 300 may be charged by grounding the effusing body 115 andkeeping the charging electrode 121 at a high voltage with a power supplyconnected to the charging electrode 121. The charging electrode 121 andthe effusing body 115 are not necessarily grounded.

The accumulating unit 128 is a member on which the nanofibers 301produced by electrostatic stretching are accumulated. In the presentembodiment, the accumulating unit 128 is a sheet member made oftungsten, which is a material for a capacitor, an electric device, andprovided as a rolled sheet, a roll 27.

The accumulating unit 128 is not limited to this. For example, theaccumulating unit 128 may be a stiff plate-like member. When only theaccumulated nanofibers 301 are used, the accumulating unit 128 may be asheet which allows easy removal of the nanofibers 301 therefrom, forexample, a fluoroplastic coated sheet or a silicon-coated sheet.

The attracting unit 104 is an apparatus which attracts the nanofibers301 produced in space to the accumulating unit 128. In the presentembodiment, the attracting unit 104 is a metal plate which alsofunctions as the charging electrode 121 and is disposed behind theaccumulating unit 128 as viewed from the effusing body 128. Theattracting unit 104 attracts the nanofibers 301 charged to theaccumulating unit 128 by an electric field. In other words, theattracting unit 104 is an electrode which generates an electric field toattract the nanofibers 301 charged.

The moving unit 129 is a device which moves at least one of the effusingbody 115 and the accumulating unit 128 relative to each other. In thepresent embodiment, the effusing body 115 is fixed and only theaccumulating unit 128 is moved by the moving unit 129. Specifically, themoving unit pulls out the accumulating unit 128 having a long length byrolling it up from the roll 127, and transfers the accumulating unit 128along with the accumulated nanofibers 301.

The moving unit 129 may not only move the accumulating unit 128 but alsomove the effusing body 115 in relation to the accumulating unit 128. Inanother example of the operation of the accumulating unit 128, themoving unit 129 may move the accumulating unit 128 in any necessarymanner. For example, the moving unit 129 may move the accumulating unit128 in a given direction to reciprocate the effusing body 115. Thedirection in which the accumulating unit 128 moves is not limited to thedirection perpendicular to the array of the openings 119 as in thepresent embodiment. The accumulating unit 128 may move in the directionalong the array of the openings 119 so that the effusing body 115reciprocates in the direction perpendicular to the array of the openings119.

Here, the solute which is to be dissolved or dispersed in the solution300 and is to be a resin contained in the nanofibers 301 is a highmolecular substance. Examples of the high molecular substance includepolypropylene, polyethylene, polystyrene, polyethylene oxide,polyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, poly-m-phenylene terephthalate, poly-p-phenyleneisophthalate, polyvinylidene fluoride, polyvinylidenefluoride-hexafluoropropylene copolymer, polyvinyl chloride,polyvinylidene chloride-acrylate copolymer, polyacrylonitrile,polyacrylonitrile-methacrylate copolymer, polycarbonate, polyarylate,polyester carbonate, polyamide, aramid, polyimide, polycaprolactone,polylactic acid, polyglycolic acid, collagen, polyhydroxybutyric acid,polyvinyl acetate, polypeptide, and a copolymer thereof. The oxide maybe the one selected from among the above substances or a mixturethereof. The substances are given for illustrative purposes only and thepresent invention is not limited to the resins.

The solvent to be used as the solution 300 may be a volatile organicsolvent. Specific examples of the solvent include methanol, ethanol,1-propanol, 2-propanol, hexafluoroisopropanol, tetraethylene glycol,triethylene dibenzyl alcohol, 1,3-dioxolane, 1,4-dioxane, methyl ethylketone, methyl isobutyl ketone, methyl-n-hexyl ketone, methyl-n-propylketone, diisopropyl ketone, diisobutyl ketone, acetone,hexafluoroacetone, phenol, formic acid, methyl formate, ethyl formate,propyl formate, methyl benzoate, ethyl benzoate, propyl benzoate, methylacetate, ethyl acetate, propyl acetate, dimethyl phthalate, diethylphthalate, dipropyl phthalate, methyl chloride, ethyl chloride,methylene chloride, chloroform, o-chlorotoluene, p-chlorotoluene,chloroform, carbon tetrachloride, 1,1-dichloroethane,1,2-dichloroethane, trichloroethane, dichloropropane, dibromoethane,dibromopropane, methyl bromide, ethyl bromide, propyl bromide, aceticacid, benzene, toluene, hexane, cyclohexane, cyclohexanone,cyclopentane, o-xylene, p-xylene, m-xylene, acetonitrile,tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxid, pyridine, and water. The oxide may be the one selected fromamong the above substances or a mixture thereof. The substances aregiven for illustrative purposes only and the solution 300 used in thepresent invention is not limited to the solvents above.

In addition, an additive of an inorganic solid material may be added tothe solution 300. The inorganic solid material may be an oxide, acarbide, a nitride, a boride, a silicide, a fluoride, or a sulfide.However, in view of preferable properties, such as thermal resistanceand workability, of the nanofibers 301 to be manufactured, an oxide ispreferable among them. Examples of the additive include Al₂O3, SiO₂,TiO₂, Li₂O, Na₂O, MgO, CaO, SrO, BaO, B₂O₃, P₂O₅, SnO₂, ZrO₂, K₂O, Cs₂O,ZnO, Sb₂O₃, As₂O₃, CeO₂, V₂O₅, Cr₂O₃, MnO, Fe₂O₃, CoO, NiO, Y₂O₃, Lu₂O₃,Yb₂O₃, HfO₂, and Nb₂O₅. The oxide may be the one selected from among theabove substances or a mixture thereof. The substances are given forillustrative purpose only and the additive to be added to the solution300 in the present invention is not limited to the substances.

The mixture ratio between the solvent and the solute in the solution 300depends on the selected solvent and the selected solute. A desirableamount of solvent accounts for approximately 60 to 98 weight percent. Apreferable amount of solute accounts for 5 to 30 weight percent.

The following describes a method of manufacturing the nanofibers 301using the nanofiber manufacturing apparatus 100.

First, the supply unit 107 supplies the solution 300 to the effusingbody 115 (a supply step). The storage tank 113 of the effusing body 115is thus filled with the solution 300.

Next, the charging power supply 122 sets the charging electrode 121 at apositive or negative high voltage. Then, charges concentrate at the tippart 116 of the effusing body 115 facing the charging electrode 121, andthe charges transfer to the solution 300 which effuses through theeffusing holes 118 into space, so that the solution 300 is charged (acharging step).

The charging step and the supply step are simultaneously performed sothat the solution 300 charged effuses from the end openings 119 of theeffusing body 115 (an effusing step).

Here, the solution 300 effusing from the openings 119 forms Taylor cones303 which cover the openings 119 and hang from the tip part 116. Each ofthe Taylor cones 303 is formed to cover a corresponding one of theopenings 119. The solution 300 forms a thread-like shape hanging downfrom the tip of each of the Taylor cones 303. The Taylor cones 303 thusformed prevent generation of ionic wind so that quality of resultingnanofibers 301 can be increased.

Next, the solution 300 flying in space for a certain distance iselectrostatically stretched so that the nanofibers 301 are produced (ananofiber producing step). Here, the solution 300 effusing is highlycharged (that is, at a high charge density) with no impact of ionic windand the solution 300 flying out of the openings 119 form thin threadswithout uniting each other in flight. Most of the solution 300 thusturns to the nanofibers 301. On the other hand, because the solution 300effusing is highly charged (that is, at a high charge density), theelectrostatic stretching repeatedly occurs so that nanofibers 301 havinga thin diameter are produced in large quantity.

In this condition, an electric field generated between the effusing body115 and the attracting unit 104 disposed behind the accumulating unit128 as viewed from the effusing body 115 attracts the nanofibers 301 tothe accumulating unit 128 (an attracting step).

The nanofibers 301 are thus accumulated on the accumulating unit 128,and then are collected (a collecting step). The accumulating unit 128 isslowly transferred by the moving unit 129 so that each of the nanofibers301 has a band-like shape extending in the direction of the transfer.

The method of manufacturing nanofibers using the nanofiber manufacturingapparatus 100 configured in the above manner enables production of highquality nanofibers 301 at high productivity, eliminating spatialunevenness.

It is to be noted that present invention is not limited to the aboveembodiment. For example, the charging electrode 121 may be disposedbetween the effusing body 115 and the accumulating unit 128 so as to beclose to the effusing body 115 as shown in FIG. 5. The nanofibermanufacturing apparatus 100 in such an embodiment may further include anaccumulating unit 128 which is air-permeable and on which nanofibers 301are accumulated, and an attracting unit 104 which generates a gas flowto converge at a predetermined part. Specifically, as shown in FIG. 5,the nanofiber manufacturing apparatus 100 may include a vacuumaspiration device 141 disposed such that the vacuum aspiration device141 functions as the attracting unit 104 by generating a gas flow whichblows from behind the accumulating unit 128 toward the accumulating unit128. In addition, the nanofiber manufacturing apparatus 100 may furtherinclude an accumulation power supply 123 provided separately from (orfunctionally integrated with) the charging power supply 122 so that thenanofibers 301 are attracted by an electric field and by a gas flow,selectively or simultaneously.

Alternatively, the effusing body 115 may have a structure which allowsdisassembly of the effusing body 115 into parts as shown in FIG. 6. Inparticular, a structure which allows disassembly so as to expose innersurfaces of the effusing holes 118 is preferable because objects in theeffusing holes 118 such as a resin adherent thereto can be easilyremoved.

The present invention is applicable to manufacture of nanofibers andspinning using nanofibers, and manufacture of unwoven fabric ofnanofibers.

REFERENCE SIGNS LIST

-   100 Nanofiber manufacturing apparatus-   104 Attracting unit-   107 Supply unit-   113 Storage tank-   114 Guide tube-   115 Effusing body-   116 Tip part-   117 Side wall part-   118 Effusing hole-   119 Opening-   121 Charging electrode-   122 Charging power supply-   127 Roll-   128 Accumulating unit-   129 Moving unit-   151 Container-   300 Solution-   301 Nanofiber

1. A nanofiber manufacturing apparatus for producing nanofibers byelectrically stretching a solution in space, the nanofiber manufacturingapparatus comprising: an effusing body including a tip part having anelongated flat face, a plurality of effusing holes terminating inopenings in an outer surface of the elongated flat face, and two sidewall parts extending along both sides of the effusing holes, the sidewall parts rising from the tip part such that the distance between theside wall parts increases in a direction away from the tip part, whereinthe openings are disposed at given intervals to form a one-dimensionalarray and the tip part has a width that is larger than a diameter of theopenings; a charging electrode disposed at a given distance from theeffusing body; and a charging power supply for applying a given voltagebetween the effusing body and the charging electrode.
 2. The nanofibermanufacturing apparatus according to claim 1, wherein the effusing bodyfurther includes: a supply unit for supplying the solution to theeffusing holes at a given pressure; and a storage tank connected to theeffusing holes, the storage tank storing the solution supplied from saidsupply unit, and supplying the solution to the effusing holes.
 3. Thenanofiber manufacturing apparatus according to claim 1, wherein the tippart has a rectangular shape having a width which is larger than adiameter of the openings provided in the tip part.
 4. The nanofibermanufacturing apparatus according to claim 1, further comprising; anaccumulating unit on which the nanofibers produced in the space areaccumulated; and an attracting unit configured to attract the nanofibersto said accumulating unit.
 5. The nanofiber manufacturing apparatusaccording to claim 4, further comprising a moving unit configured tomove at least one of the effusing body and the accumulating unitrelative to each other.
 6. The nanofiber manufacturing apparatusaccording to claim 1, wherein the effusing body has a structure whichallows (i) disassembly of the effusing body into parts to exposesurfaces forming the effusing holes and (ii) re-assembly of the partsinto the effusing body.
 7. The nanofiber manufacturing apparatusaccording to claim 1, wherein the tip part has a smooth surface whichfills the intervals between the openings.